1. Field of the Invention
The present invention relates to electro-optics, and, in particular, to the configuration of optoelectronic devices such as electro-absorption modulated lasers for packaging and use, for example, in optical communication systems.
2. Description of the Related Art
An electro-absorption modulated laser (EML) is an integrated device having a laser portion that converts an electrical signal into an optical light signal and a modulator portion that modulates the optical signal generated by the laser portion based on electrical signals received from an electrical signal generator, e.g., to encode information into the optical signal for transmission over an optical fiber in an optical communication system. In order to reduce return loss due to electrical reflections, it is important match the output impedance of the electrical signal generator to the input impedance of the EML device.
FIG. 1 shows a schematic diagram of a conventional configuration of an EML device 102 mounted onto a submount 104 and ready for assembly as a packaged device. As shown in FIG. 1, submount 104 has a modulator signal electrode 106 to which an electrical signal generator is to be connected and a ground electrode 108 with an integrated resistor 110, while EML device 102 has a modulator contact pad 112 located adjacent to the modulator portion of the EML device. According to a conventional wiring configuration, modulator signal electrode 106 is connected to modulator contact pad 112 by a first wire 114, and modulator contact pad 112 is in turn connected to integrated resistor 110 of ground electrode 108 by a second wire 116. With this wiring configuration, modulator signal electrode 106 can be connected to an external electrical signal generator (not shown) to drive the modulator portion of EML device 102.
Standard electrical signal generators for EML devices, such as EML device 102 of FIG. 1, have a 50-ohm output impedance. As shown in FIG. 1, integrated resistor 110, which also has a 50-ohm impedance, is connected between modulator contact pad 112 and ground electrode 108 in order to match the impedances between EML device 102 and a standard electrical signal generator. Wires 114 and 116 add inductances to the circuitry that can affect the high-frequency performance of the final packaged device. In conventional configuration schemes, wires 114 and 116 are purposely selected to be the same length (e.g., 1.25 millimeters), so that the inductances added to the resulting circuit by the two wires will have the same magnitude (e.g., 1.25 nanohenries (nH), where standard gold wiring adds about 1 nH of inductance for every 1 mm of length). Such a wiring scheme may be referred to as symmetric inductive peaking, since the wiring is attached in a symmetric manner that keeps inductance levels the same in an attempt to optimize the performance of the resulting packaged device.